The increasing availability of low-cost, full-color imaging devices such as laser and inkjet printers and off-the-shelf imaging software has lead to an increase in counterfeiting of paper-based currency. The treasury departments of governments across the world in conjunction with imaging product manufacturers have taken steps to reduce counterfeiting.
One approach is to identify the imaging devices used to make counterfeit currency. For example, color copiers and printers typically print an invisible watermark that includes a serial number associated with that particular copier or printer. When a copy or print is made with such a copier or printer, the invisible watermark can be decoded in order to read the serial number. Such an approach, however, typically only helps in identifying the imaging device used to make that copy or print.